Description
GPS Aided Geo Augmented Navigation (GAGAN) is a Space-Based Augmentation System (SBAS) developed for the Indian region and standardized within 3GPP for integration with cellular networks. It enhances the performance of the Global Positioning System (GPS) by providing correction data and integrity information via geostationary satellites. The system consists of a network of ground reference stations that monitor GPS signals, master control centers that process the data to generate correction messages, and uplink stations that transmit these messages to geostationary satellites for broadcast to users.
Within the 3GPP architecture, GAGAN is relevant to location services, particularly for Assisted-GNSS (A-GNSS) features. The specifications define how GAGAN augmentation data can be delivered to user equipment (UE) via cellular networks to improve positioning accuracy and time-to-first-fix. The system works by measuring errors in the GPS signals caused by ionospheric delays, satellite clock inaccuracies, and orbital deviations. These error corrections are computed at the ground segment and then broadcast, enabling receivers to achieve positional accuracy within a few meters, which is critical for safety-of-life applications like aviation navigation.
Key components include the GAGAN Signal-in-Space (SIS), which broadcasts the correction messages on the L1 frequency (1575.42 MHz), and the network of Indian Reference Stations (INRES). In 3GPP contexts, protocols such as Radio Resource Control (RRC) and LTE Positioning Protocol (LPP) may carry GAGAN assistance data to UEs. The role of GAGAN in mobile networks is to provide a reliable, high-accuracy positioning source that complements other methods like Observed Time Difference of Arrival (OTDOA) or sensor fusion, especially in regions where GAGAN coverage is available. This integration supports applications requiring precise location, such as emergency services, navigation, and geofencing.
Purpose & Motivation
GAGAN was developed to address the limitations of standalone GPS, which lacks sufficient accuracy, integrity monitoring, and availability for critical applications like aircraft navigation over Indian airspace. GPS alone can have errors of up to 10 meters or more due to atmospheric effects and satellite clock errors, which are unacceptable for precision approaches in aviation. The motivation was to create a regional augmentation system that meets the stringent requirements of the International Civil Aviation Organization (ICAO) for Safety of Life (SoL) services.
Historically, other regions developed similar SBAS like WAAS (USA), EGNOS (Europe), and MSAS (Japan). For India, GAGAN provided a tailored solution to enhance GPS performance over its geographical area, including remote and oceanic regions. Its integration into 3GPP standards, starting from Release 8, allowed mobile networks to leverage this enhanced positioning capability, enabling new services that demand high accuracy and reliability. This addressed the previous limitation where cellular positioning methods alone could not achieve the sub-meter accuracy required for applications like autonomous vehicles, precision agriculture, and advanced driver-assistance systems (ADAS).
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (23 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, new support was introduced for OTDOA (Observed Time Difference of Arrival) positioning in NR (New Radio). The enhancements included the ability to request OTDOA assistance data specifically for NR, and the expansion of this assistance data to include TDD UL/DL configuration details and SFN offset information. Furthermore, support for an Inertial Measurement Unit (IMU) was introduced to aid the OTDOA procedure.
In Release 16, the key updates for A-GNSS included the formal introduction of support for the B1C signal from the BeiDou Navigation Satellite System (BDS) and an update to the Interface Control Document (ICD) for the B1I signal to version 3.0. Furthermore, the release enhanced Observed Time Difference of Arrival (OTDOA) positioning by specifying support for assistance data when the serving cell is a New Radio (NR) cell. These changes expanded signal compatibility and refined positioning procedures for 5G networks.
- Introduction of B1C signal in BDS system in A-GNSS TS 36.305CR0083
- Introduction of B1C signal in BDS system in A-GNSS TS 37.355CR0248
- Introduction of B1C signal in BDS system in A-GNSS TS 38.305CR0013
- Update B1I signal ICD file to v3.0 in BDS system in A-GNSS TS 36.305CR0088
- Update B1I signal ICD file to v3.0 in BDS system in A-GNSS TS 37.355CR0259
- Update B1I signal ICD file to v3.0 in BDS system in A-GNSS TS 38.305CR0024
+ 3 more changes
In Release 17, the 3GPP specification introduced a clarification for the GAGAN function regarding the Galileo navigation message within the GNSS navigation model. Specifically, the update clarified the signal reference for the State Space Representation (SSR) clock corrections. This refinement ensured unambiguous interpretation of the Galileo SSR data for augmented navigation systems like GAGAN.
- Clarifying Galileo NAV message in the GNSS Navigation model to clarify SSR clock correction signal reference TS 37.355CR0412
In Release 18, the updates to the GAGAN function consisted of specific corrections. These included fixes to the GNSS-AlmanacSupport and GNSS-UTC-ModelSupport capabilities used in A-GNSS positioning, as well as editorial corrections to the related navigation pane descriptions.
In Release 19, the GAGAN function was enhanced to support new global navigation satellite systems by introducing A-GNSS assistance for the NavIC L1 SPS signal and the BeiDou B2b signal. This support was formally integrated into the core network and positioning protocols, specifically within the LTE and NR Stage 2 specifications as well as the LPP and TS 38305 documents. These additions expanded the range of satellite signals available for assisted positioning in user equipment.
- Introduction of NavIC L1 SPS A-GNSS in LTE Stage 2 specification TS 36.305CR0120
- Introduction of BDS B2b in A-GNSS TS 36.305CR0121
- Introduction of NavIC L1 SPS A-GNSS in LPP TS 37.355CR0532
- Introduction of B2b signal in BDS system in A-GNSS TS 37.355CR0545
- Introduction of NavIC L1 SPS A-GNSS in NR Stage 2 specification TS 38.305CR0179
- Introduction of BDS B2b in A-GNSS for TS 38305 TS 38.305CR0180
Explore further
Broader topics and technologies where GAGAN plays a role.
Defining Specifications
3GPP specifications that define or reference GAGAN, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 22.071 vj00 | 3GPP TS 22.071: Location Services (LCS) Stage 1 | Rel-19 |
| TS 25.305 vj00 | UTRAN UE Positioning Stage 2 | Rel-19 |
| TS 25.331 vj00 | UTRAN RRC Protocol Specification | Rel-19 |
| TS 25.423 vj00 | UTRAN RNSAP Specification | Rel-19 |
| TS 25.433 vj00 | Node B Application Part (NBAP) Protocol | Rel-19 |
| TS 25.453 vj00 | PCAP Protocol Specification | Rel-19 |
| TS 36.305 vj00 | UE Positioning in E-UTRAN Stage 2 | Rel-19 |
| TS 36.355 vj00 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 37.355 vj20 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 38.305 vj00 | NG-RAN UE Positioning Stage 2 | Rel-19 |
| TS 38.455 vj10 | NR Positioning Protocol A (NRPPa) | Rel-19 |
| TS 44.031 vj00 | Radio Resource LCS Protocol (RRLP) | Rel-19 |